Field of the Invention
The solution according to one or more embodiments of the invention generally relates to wireless communication networks. More particularly, the proposed solution relates to an advanced receiver architecture applicable in wireless communication networks based on OFDM (“Orthogonal Frequency Division Multiplexing”) and MIMO (“Multiple Input Multiple Output”) techniques—such as LTE (“Long Term Evolution”), LTE-Advanced and WiMAX (“Worldwide Interoperability for Microwave Access”) networks.
Overview of the Related Art
Evolution of wireless communications has experienced significant growth in terms of spread and performance, and has recently brought to 3GPP LTE (“Third Generation Partnership Project Long Term Evolution”)/LTE-Advanced and WiMAX standards.
Such standards are conceived for allowing high-speed transmissions.
In order to achieve that, a combination of OFDM and MIMO techniques is used for transmission. According to OFDM technique, bits to be transmitted are split into bits sequences, then the bits sequences are modulated by separate and reciprocally orthogonal sub-carriers and multiplexed into OFDM symbols for transmission. According to MIMO technique, multiple OFDM symbols are transmitted/received via multiple transmitting/receiving antennas.
As known, spectral efficiency of modern wireless communication networks is severely limited by inter-cell interference (i.e., the interference originated by adjacent cells on the cell which a serving transmitter belongs to), especially for users located at cell edges. For this reason, modern wireless communication networks provide, before transmission, OFDM symbols encoding that exploits the availability of multiple transmitting/receiving antennas, such as SFBC (“Space Frequency Block Code”) or STBC (“Space Time Block code”) encoding (based on the application of the Alamouti algorithm in the frequency or time domains, respectively) in case of two transmitting antennas, or SFBC-FSTD (“SFBC-Frequency Switching Transmit Diversity”) encoding in case of four transmitting antennas.
SFBC/STBC-based or SFBC-FSTD-based MIMO OFDM techniques require additional computational capabilities in order to correctly decode, at user terminal side, the transmitted bits.
This is exacerbated in modern scenarios, wherein the growing number of wireless communication networks users, as well as the growing demand for services requiring very high data traffic (such as internet, multimedia and real-time services) and the evolution of mobile applications, require higher and higher user data rates.
In the state of the art, different algorithms (and/or receiver architectures implementing them) intended to improve decoding of the transmitted bits are proposed.
S. M. Alamouti, “A Simple Transmit Diversity Technique for Wireless Communications”, IEEE Journal on Select Areas in Communications, vol. 16, no. 8, October 1998, describes the principles of the space/time algorithm devised by Alamouti.
Y. Ohwatari, et al, “Investigation on Advanced Receiver Employing Interference Rejection Combining for Space-Frequency Block Code Transmit Diversity in LTE-Advanced Downlink”, 2012 IEEE 23rd International Symposium on Personal, Indoor and Mobile Radio Communications—(PIMRC), discloses the application of the MMSE-IRC algorithm for the specific case of SFBC transmission in the LTE/LTE-Advanced system. The MMSE-IRC algorithm provides superior performance compared to the Alamouti algorithm in the presence of colored (i.e. correlated) interference. Besides, the paper provides a method for the estimate of the spatial correlation matrix of the interference based on Reference Signals (RS) provided in LTE/LTE-Advanced system.
WO 2008/069467 discloses an iterative receiver comprising a signal detector estimating interference from an estimated transmitted signal, and canceling the estimated interference from a signal received through an antenna; a decoder performing channel decoding by using the interference cancelled received signal; a soft decision unit performing a soft decision process on the transmitted signal by using the channel decoded signal; a channel estimator estimating a channel by using the soft decision applied transmitted signal and the received signal; a covariance estimator estimating covariance on the sum signal of the interference and noise by using the soft decision applied transmitted signal, the received signal, and the estimated channel; and a hard decision unit determining the transmitted signal by using the channel decoded signal after interference cancellation, channel decoding, estimated transmitted signal updating, channel estimation, and covariance estimation are iterated a number of times.
S. T. Brink et Al., “Iterative Demapping and Decoding for Multilevel Modulations”, IEEE 1998, discloses the architecture of an iterative receiver wherein symbol-to-bit demapping and channel decoding operations are executed iteratively.